KM prevents unmount disk

Basic Problem
When I attempt to unmount the internal HD I get an error message saying that the disk can’t be unmounted because KM is using it. Why does this occur and how do I stop it?

I’m attempting to run my iMac from an external SSD.
As part of that process I want to unmount the internal drive so that it doesn’t consume resources ( I notice that I can hear the internal drive working even though I’m booted from the external SSD).
Using Disk Utility to unmount the internal HD fails as noted above.
So I’m wondering why KM would be in use on the internal HD when that isn’t the boot drive ? Does KM have some monitoring facility whereby it is constantly monitoring the system, rather in the same way that Hazel monitors folders?
I’d appreciate any thoughts on why KM is still active on the internal drive and how to shut it down so that I can unmount the disk.


It’s possible you have the background Keyboard Maestro Engine on that internal drive. You may need to launch the KM Editor then select File > Quit Engine. If that resolves the issue and the internal disk unmounts, try then toggling the Keyboard Maestro preference for Launch Engine At Login off then on.

You can use the Terminal command:


to see what open files there are.

If the system is saying it’s Keyboard Maestro, then you can do something like:

lsof | grep Maestro

Generally the only files Keyboard Maestro would have open would be in the application itself, so @NaOH’s suggestion that the Engine (or Editor) is running from the specified disk would be like.